A multi-stage forging apparatus fabricating various component parts like bolts, nuts, etc. has a base frame and stepwise forges a work being fed at one side end portion of the base frame as a raw material having a rough shape into a finished product having a refined shape throughout a plurality of forging stations each provided with a die and a punch. The work is forged at respective forging station and pushed out of the die of each station by means of a knockout pin installed in each die. The forging apparatus is further provided with a work transfer having a plurality of chucks for grasping and transferring the works from one forging station to subsequent other forging station.
Conventionally, the work transfer has a chuck reciprocating mechanism for transferring the work between the adjacent dies, and in an operation of the chuck reciprocating mechanism, the chuck reciprocates in a single direction in which the dies are aligned, i.e., after grasping the work in front of an upstream did the chuck moves to a front of a downstream die, and then, after releasing the work there it returnes to the front of the upstream die.
On the other hand, in case of forging such a specific work, a housing of an ignition plug, for instance, that a length of the work is relatively short and a diameter of the work becomes smaller as it goes to a rear end portion thereof, when the work is so pushed out from a bore of the die that most part of it comes out of the die, the work is likely to be tilted relative to the die with its head down under gravity. Therefore, it is possible that the chuck of the work transfer may fail to grasp the work, and even if the work is grasped, since it is not in a correct horizontal posture but tilted the work may not be driven into a bore at the next die properly or smoothly by only the forging motion of the punch.
To avoid this disadvantage, Japanese Examined Patent Publication No. 48294/1982 or Japanese Examined Utility Model Patent Publication No. 42358/1990 discloses a work transfer having a work extract-insert function relative to the die, which is operated as follows:
A chuck of the work transfer grasps the work of such specific shape as mentioned above at a time that the work is not wholly pushed out of the upstream die by the knockout pin, and the chuck recedes from a front face of the upstream die keeping the grasp of the work. Then, the chuck moves to the front of the downstream die, and approaches to a front face of the downstream die keeping the grasp of the work. Therefore, the work is, at the upstream die, extracted from the die bore by the chuck before it is tilted, and, at the downstream die, the work is inserted into the die bore to some extent by the chuck before it is fully driven into the die bore by the forging motion of the punch.
However, the chuck employed in the work transfer disclosed in the above-mentioned Publications is a press type chuck that has a pair of finger members arranged to face each other leaving a predetermined spacing therebetween, and the work is pushed out of the die and pressed into the spacing between the finger members so that it should be grasped by the finger members at its portion where a diameter is larger than a breadth of the spacing.
Therefore, in case of forging and grasping still such a specific a work, a bottom plate Z for a speaker as shown in FIG. 15, for instance, that has a stepped surface, diameter of each stepped portion being different and becoming smaller as it goes to a rear end portion thereof, and the work has a thin flange X1 of bigger diameter at its front portion, a relatively longer tubular midportion X2 of smaller diameter and a relatively shorter tubular rear portion X3 of still further smaller diameter, it is possible that the press type chuck as mentioned above may not grasp the work stably because the front flange portion X1 of the work is too thin for the chuck to catch steadily while the chuck is to grasp the work at that flange portion X1. As a result, it is inevitable that the chuck should grasp the work Z at the longer midportion X2 instead of the thin front flange portion X1, but above-mentioned press type chuck is, as clearly understood, not structurally able to comply with this desire.
In order to overcome this problem, as also disclosed in the above Japanese Examined Utility Model Patent Publication No. 42358/1990, an open-close type chuck may be employed, in which the finger members are swingably supported respectively so as to open for releasing the work and to close for grasping the work. However, in order to employ this open-close type chuck, in addition to the chuck reciprocating mechanism for the work transfer function and to the chuck approach-recede mechanism for the work extract-insert function, another chuck open-close mechanism for the work grasp-release function is required, which extremely complicates a whole structure of the work transfer.